A safety device for an injection device is already known, such as that described in document FR 2 830 765. that is provided with a syringe carrying a needle and a sheath for protecting the needle. The sheath may occupy an injection position, leaving the needle uncovered, or a safe position, in which it covers the needle. The sheath is driven by a spring that is compressed while the sheath is in the injection position and that is expanded while the sheath is in the safe position. In order to control the movement of the spring, the safety device is provided with retractable tabs holding the spring in the compressed position during injection.
Prior to being used, the safety device is generally stored in its injection position, and thus in a position in which the spring is under stress.
It is found that the retractable tabs retaining the spring can become damaged by wear while the device is in storage, particularly since storage may last for several years. More precisely, the retractable tabs are often made of a flexible plastics material and can suffer a certain amount of creep over time, particularly since they are subjected to tension from the compressed spring applying a certain amount of stress thereto. As a result, the safety device might become faulty if it is not used within a certain length of time.
A particular object of the invention is to resolve that drawback by proposing a safety device that is guaranteed to operate properly even after being stored for a relatively long time prior to use.